Vaccination is the most important public health measure for preventing disease caused by annual epidemics of influenza. The effective use of vaccines is dependent on being able to quickly produce large quantities of vaccine material (e.g., virus) from a stable and easy to cultivate source. The rapid development of vaccines and their abundant availability is critical in combating many human and animal diseases. Delays in producing vaccines and shortfalls in their quantity can cause problems in addressing outbreaks of disease. For example, recent studies suggest that there is cause for concern regarding the long lead times required to produce vaccines against pandemic influenza. See, for example, Wood, J. M., 2001, Philos. Trans. R. Soc. Lond. B. Biol. Sci., 356:1953. Efficient vaccine production requires the growth of large quantities of vaccine material produced in high yields from a host system. Different vaccine materials require different growth conditions in order to obtain acceptable yields. Vaccine material may be produced in embryonated eggs, primary tissue culture cells, or in established cell lines. However, these host systems currently suffer from a number of limitations detailed below.
Embryonated eggs are typically used for influenza vaccine virus production in a time-, labor-, and cost intensive process that necessitates the management of chicken breeding and egg fertilization. In addition, influenza vaccine produced in eggs is contraindicated for persons with egg allergies due to the severe immediate hypersensitivity reaction that can occur. Thus, there has been an effort by the vaccine industry to develop alternative production platforms that do not utilize eggs such as producing influenza vaccine in a cell culture system.
The use of primary tissue culture cells is hampered by the difficulties encountered in developing and maintaining a stable primary cell population. Often established cells lines are used to circumvent the technical limitations of primary cells. However, many of these cell lines are known to be tumorigenic and as such raise safety concerns and are subject to significant regulatory constraints against their use for vaccine production. In fact, the applicable guidelines of the World Health Organization indicate that only a few cell lines are allowed for vaccine production. Additional problems arise from the use of serum and/or protein additives derived from animal or human sources in cell culture media. For example, variability in the quality and composition among lots of additives and the risk of contamination with mycoplasma, viruses, BSE-agents and other infectious agents are well known. In general, serum or serum-derived substances like albumin, transferrin or insulin may contain unwanted agents that can contaminate the culture and the biological products produced from therefrom. Therefore, many groups are working to develop efficient host systems and cultivation conditions that do not require serum or serum derived products.
Consequently, there has been a demand for establishing a non-tumorigenic cell line useful for the production of vaccine materials in a low-cost, highly safe and stable manner preferably in serum-free or in animal protein-free culture conditions. Such a cell system would be particularly useful for the production of influenza vaccine material.
Madin Darby Canine Kidney (MDCK) cells have been traditionally used for the titration of influenza viruses (Zambon M., in Textbook of Influenza, ed Nicholson, Webster and Hay, ch 22, pg 291-313, Blackwell Science (1998)). These cells were established in 1958 from the kidney of a normal male cocker spaniel. The ATCC list the MDCK (CCL 34) line as having been deposited by S. Madin and N. B. Darby however, numerous other lineages of MDCK cells are available. Leighton J and his coworkers published a series of papers (Leighton et al., 1968, Science 163:472; Leighton et al., 1970, Cancer 26:1022 and Leighton et al., 1971 Europ J. Cancer 8:281) documenting the oncogenic characteristics of the MDCK cells. However, the lineage and passage number of the MDCK cells used for these studies was not described and it was already known that MDCK cells from different lineages and different passages showed changes in chromosome numbers and structure (Gaush et al., 1966, Proc. Soc. Exp. Biol. Med., 122: 931) which could result in cells with tumorigenic properties.
Since one of the major considerations for the acceptability of a cell line for vaccine production concerns the potential malignancy of those cells the use of MDCK cells for the production of vaccine material using currently described cell lines is limited. Groner et al. (U.S. Pat. No. 6,656,720) and Makizumi et al. (U.S. Pat. No. 6,825,036) both purport to disclose cell lines derived from MDCK cells which have been adapted to grow in serum-free media in suspension and which can be utilized for the production of influenza virus. However, it has been reported that there is correlation between the loss of anchorage requirement and the transformation of normal animal cells to cells which are tumorigenic (Stiles et al., 1976, Cancer Res., 36:3300). Several groups (Kessler et al., 1999, Cell Culture Dev Biol Stand, 98:13; Merten et al., 1999, Cell Culture Dev Biol Stand, 98:23 and Tree et al., 2001, Vaccine, 19:3444) purport to describe the use of MDCK cells for the large-scale production of influenza virus; however, they do not address the potential transformation of the MDCK cells used.
Citation or discussion of a reference herein shall not be construed as an admission that such is prior art to the present invention. In addition, citation of a patent shall not be construed as an admission of its validity.